2nd order observations with FORS2 and grisms 600z & 600I:
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Thomas Szeifert
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Stgo. 2001-12-10
----------------


Here the 2nd order response of all instrument:
For one incoming photon below the slit you would detect 5.43577e-02 
electrons at 3800\AA with grism 600I (in average) on the SITE CCD. 
For more realistic observation setups a slit loss has to be considered 
depending on seeing and slit width. Please note that for all other
grisms we have given the response of the grism alone as measured in the 
lab while we give below the full instrument throughput as measured on 
the sky with a 5 arcsecond slit.
  
The performance in 2nd order observations is relatively low, but one
would typically get a bit more flux then in Echelle mode. The final 
solution would be to purchase a 1200 grooves per mm grims at a central 
wavelength of about 4300 Angstroem which has to be of volume phased 
holographic type since the "groove" size is of the order of the wavelength.
This would be a factor of ~3 better in response then the 2nd order setup.
Unfortunately this type of grism is not on the market and has to 
be designed within ESO first,... (We'll announce the project on the
FORS main page once we know more about the feasibility and after the 
purchase order has been sent out - TSz 2001-12-10).


GRISM 600I+25

lambda       response
\AA          e-/photon
------------ ------------ 
 3.80000e+03  5.43577e-02 
 3.83000e+03  6.57221e-02 
 3.86000e+03  7.42660e-02 
 3.89000e+03  8.04071e-02 
 3.92000e+03  8.45633e-02 
 3.95000e+03  8.71527e-02 
 3.98000e+03  8.85930e-02 
 4.01000e+03  8.93022e-02 
 4.04000e+03  8.96981e-02 
 4.07000e+03  9.00839e-02 
 4.10000e+03  9.04050e-02 
 4.13000e+03  9.05369e-02 
 4.16000e+03  9.03556e-02 
 4.19000e+03  8.97366e-02  
 4.22000e+03  8.85558e-02   
 4.25000e+03  8.66888e-02   
 4.28000e+03  8.40120e-02  
 4.31000e+03  8.06262e-02  
 4.34000e+03  7.71821e-02  
 4.37000e+03  7.44131e-02  
 4.40000e+03  7.30511e-02  
 4.43000e+03  7.33230e-02  
 4.46000e+03  7.42172e-02  
 4.49000e+03  7.45360e-02  
 4.52000e+03  7.30939e-02  
 4.55000e+03  7.01658e-02  
 4.58000e+03  6.88311e-02  
 4.61000e+03  6.17837e-02  
 4.64000e+03  5.92513e-02  
 4.67000e+03  6.75284e-02  
 4.70000e+03  6.39136e-02  
 4.73000e+03  6.11063e-02  




GRISM 600z+23

lambda       response
\AA          e-/photon
------------ ------------
 4.05000e+03  3.25149e-02
 4.15000e+03  3.96037e-02
 4.25000e+03  5.21696e-02
 4.35000e+03  6.28524e-02
 4.45000e+03  7.17043e-02
 4.55000e+03  7.90319e-02
 4.65000e+03  8.48050e-02
 4.75000e+03  8.89040e-02
 4.85000e+03  8.24789e-02
 4.95000e+03  7.74462e-02
 5.05000e+03  8.06724e-02
 5.15000e+03  6.70415e-02
 5.25000e+03  4.90414e-02